Method to fabricate small dimension devices for magnetic recording applications

ABSTRACT

A three step ion beam etch (IBE) sequence involving low energy (&lt;300 eV) is disclosed for trimming a sensor critical dimension (free layer width=FLW) to less than 50 nm. A first IBE step has a steep incident angle with respect to the sensor sidewall and accounts for 60% to 90% of the FLW reduction. The second IBE step has a shallow incident angle and a sweeping motion to remove residue from the first IBE step and further trim the sidewall. The third IBE step has a steep incident angle to remove damaged sidewall portions from the second step and accounts for 10% to 40% of the FLW reduction. As a result, FLW approaching 30 nm is realized while maintaining high MR ratio of over 60% and low RA of 1.2 ohm-μm 2 . Sidewall angle is manipulated by changing one or more ion beam incident angles.

FIELD OF THE INVENTION

The invention relates to a method of trimming the critical dimension(CD) of a magnetoresistive sensor, and in particular, to a multi-stepion beam etch (IBE) process for trimming the sidewall of a giantmagnetoresistive (GMR) element or a tunneling magnetoresistive (TMR)element while maintaining a high magnetoresistive ratio (dR/R) and othermagnetic properties.

BACKGROUND OF THE INVENTION

A magnetic tunnel junction (MTJ) element also referred to as a sensor isa key component of magnetic recording devices. There is a continuouspush to increase recording density which requires the sensor to becomesmaller in order to meet high performance demands of new devices. Thereare several ways to generate sensors with a smaller CD. One is to reducethe CD by shrinking the mask dimension in the pattern that is printedinto a photoresist mask layer. Subsequently, the mask pattern istransferred through a MTJ stack of layers with an etch process toproduce a plurality of MTJ elements with a CD similar to that in thephotoresist pattern. Secondly, once the MTJ element is defined by thepattern transfer process, a reactive ion etch (RIE) may be used to trimthe sidewalls and thereby shrink the dimension of the sensor. However,both of these methods have practical limits and cannot reproduciblygenerate a CD less than about 50 nm which is needed in high performancerecording devices.

A MTJ element may be based on a TMR effect wherein a stack of layers hasa configuration in which two ferromagnetic layers are separated by athin non-magnetic dielectric layer. In a GMR sensor, the non-magneticspacer is typically Cu or another non-magnetic metallic layer. In asensor, the MTJ element is formed between two shields. A MTJ stack oflayers that is subsequently patterned to produce a MTJ element may beformed in a so-called bottom spin valve configuration by sequentiallydepositing a seed layer, an anti-ferromagnetic (AFM) pinning layer, aferromagnetic “pinned” layer, a thin tunnel barrier layer, aferromagnetic “free” layer, and a capping layer on a substrate. The AFMlayer holds the magnetic moment of the pinned layer in a fixeddirection. The free layer has a magnetization that is able to rotate andthereby establish two different magnetic states. Alternatively, the MTJelement may have a top spin valve configuration wherein a free layer isformed on a seed layer followed by sequentially forming a tunnel barrierlayer, a pinned layer, AFM layer, and a capping layer, for example.

A routine search of the prior art revealed the following references.U.S. Pat. No. 7,438,982, U.S. Pat. No. 7,616,404, U.S. Pat. No.7,615,292, and U.S. Patent Application 2008/0078739 all relate to theuse of IBE at certain incident angles to modify a surface of a magneticrecording medium but do not teach about shaping sensor sidewalls.

U.S. Pat. No. 7,561,384 discloses a method of patterning a sensor byemploying two IBE steps where the second step involves an incident anglegreater than the incident angle used in the first step. The second IBEstep removes redeposited material from the first IBE step. However, thisreference does not address any detrimental effect the second IBE stephas on the magnetic properties of sensor layers.

None of the prior art methods provide a solution for achieving a highperformance sensor CD less than 50 nm in a reliable manner by trimming asidewall of a MTJ element. Therefore, a new method is required in orderto enable further advances in magnetic recording devices.

SUMMARY OF THE INVENTION

One objective of the present invention is to provide a method forshrinking sensor CD, and in particular, reducing free layer width (FLW)to substantially less than 50 nm.

A second objective of the present invention is to provide a method forshrinking FLW to less than 50 nm according to the first objective whilemaintaining a high magnetoresistive ratio and other magnetic propertiesof the sensor.

A third objective of the present invention is to provide a method forshrinking a sensor CD that also enables the junction slope to be easilymanipulated.

According to a preferred embodiment, these objectives are achieved byinitially depositing a MTJ stack of layers on a substrate such as afirst shield in a read head. The MTJ stack of layers may have a bottomspin valve, top spin valve, or dual spin valve configuration with acapping layer as the uppermost layer in the stack. A photoresist layeris coated on the capping layer and patterned with a conventional processto form a plurality of MTJ shapes in the form of islands having acircular or oval shape, for example, from a top view. The pattern in thephotoresist mask layer is then transferred through the MTJ stackpreferably by a reactive ion etch (RIE) process to generate a MTJelement having a sidewall and a first width along a plane that willbecome the air bearing surface (ABS) in the final recording device.

A key feature of the present invention is a multiple step IBE processthat trims the sidewall and first width to a substantially smaller widthwhile maintaining MR ratio and other magnetic properties in the MTJstack. In one embodiment, the MTJ stack has a TMR configuration whereina non-magnetic spacer made of a dielectric material is formed between apinned layer and a free layer. Alternatively, the MTJ stack may have aGMR configuration with a non-magnetic metal layer formed between thefree layer and pinned layer.

The first step in the multiple step IBE process sequence comprises a lowincident angle IBE condition of less than 20 degrees with respect to aplane perpendicular to the planes of the MTJ stack of layers. The inertgas ions comprised of Ar or the like have a low energy (<300 eV) andtrim the free layer width (FLW) to a second width that representsremoval of about 60% to 90% of the total MTJ width to be trimmed duringthe entire IBE process sequence. Thereafter, a second IBE step isperformed with low energy (<300 eV) and a high incident angle of greaterthan 60 degrees from the perpendicular plane in a sweeping motion. Theion beam is moved back and forth a plurality of times over the sidewallsof the MTJ element to further trim FLW to a third width and clean upredeposited material remaining from the first IBE step. Next, a thirdIBE step comprising a low energy (<300 eV) and low incident angle ofless than 20 degrees from the perpendicular plane is employed to trimFLW to a final width that represents removal of about 10% to 40% of thetotal MTJ width to be trimmed in the entire IBE etch sequence. Acritical function of the third IBE step is to remove damaged portions ofthe sidewall that were created during the second IBE step. The componentof the ion beam directed perpendicular to the MTJ sidewalls issufficiently weak that damage to the MTJ layers is not significant. As aresult, up to about 20 nm may be trimmed during the multiple IBE stepsto shrink the FLW (first width) from around 50 nm to a final width ofabout 30 nm, for example.

Thereafter, conventional processing is employed to form an insulationlayer adjacent to the sidewalls of the MTJ. A hard bias layer forproviding longitudinal bias to the free layer in the MTJ is typicallyformed proximate to the MTJ element. Leads are formed that makeelectrical contact with the top surface of the MTJ and a second shieldis deposited above the MTJ stack.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a MTJ element during a first IBEetch step according to the present invention in which ions are directedat a steep angle with respect to sidewalls of a MTJ element to trim aninitial critical dimension (FLW) to a smaller width.

FIG. 2 is cross-sectional view of the trimmed MTJ element after thefirst IBE step and during a second IBE step at low energy and with lowincident angle with respect to the MTJ sidewalls that removes residuefrom the first IBE step and further trims the CD of the MTJ element.

FIG. 3 is a top view showing the sweeping motion around the MTJ elementduring the second IBE step that removes residue from the first IBE etchstep.

FIG. 4 is a cross-sectional view of the trimmed MTJ element after thesecond IBE step and during a third IBE step at low energy and with highincident angle with respect to the MTJ sidewalls that further trims theMTJ element to a final FLW.

FIG. 5 is a cross-sectional view of a MTJ element having a substantiallyreduced FLW following an IBE etch sequence of three steps according toan embodiment of the present invention.

FIG. 6 is a cross-sectional view of a read head where a sensor trimmedby a multiple step IBE sequence of the present invention is formedbetween two hard bias layers.

FIG. 7 is a graph that depicts the relationship between the CD of theinitially formed Photo CD in a photoresist mask and the free layer width(FLW) in the MTJ following transfer of the photoresist CD through a MTJstack of layers and trimming the CD with a three step IBE sequenceaccording to a method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a method of trimming the sidewall and a freelayer width (FLW) in a MTJ element (magnetoresistive sensor) such that aFLW of substantially less than 50 nm is achieved while maintaining themagnetic properties of the sensor. Although a bottom spin valvestructure is depicted in the exemplary embodiment, the present inventionalso encompasses top spin valve and dual spin valve configurations. Notethat a sidewall of a MTJ element is used in a singular context as it isunderstood to be a continuous boundary around a patterned MTJ. Only oneMTJ element is shown in the drawings although those skilled in the artwill appreciate that a plurality of MTJ elements arranged in rows andcolumns are formed in a typical device pattern.

Referring to FIG. 1, a portion of a partially formed magnetoresistivesensor 1 of the present invention is shown from the plane of an airbearing surface (ABS). There is a substrate 10 that in one embodiment isa bottom lead otherwise known as a bottom shield (S1) which may be aNiFe layer about 2 microns thick that is formed by a conventional methodon a substructure (not shown). It should be understood that thesubstructure may be comprised of a wafer made of AlTiC, for example.Substrate 10 may also be a composite (not shown) having a bottom S1shield and an upper gap layer wherein a top surface of the gap layercontacts seed layer 11.

A MTJ stack of layers is formed on the substrate 10 and in the exemplaryembodiment has a bottom spin valve configuration wherein a seed layer11, AFM layer 12, pinned layer 13, non-magnetic spacer 14, free layer15, and capping layer 16 are sequentially formed on the substrate. Theseed layer 11 may be comprised of Ta/Ru, Ta, Ta/NiCr, Ta/Cu, Ta/Cr orother materials typically employed to promote a smooth and uniform grainstructure in overlying layers. Above the seed layer 11 is an AFM layer12 used to pin the magnetization direction of the overlying pinned layer13, and in particular, the outer portion or AP2 layer (not shown). TheAFM layer 12 may have a thickness from 40 to 300 Angstroms and ispreferably comprised of IrMn. Optionally, one of PtMn, NiMn, OsMn, RuMn,RhMn, PdMn, RuRhMn, or MnPtPd may be employed as the AFM layer.

The pinned layer 13 preferably has a synthetic anti-parallel (SyAP)configuration represented by AP2/Ru/AP1 where a coupling layer made ofRu, Rh, or Ir, for example, is sandwiched between an AP2 layer and anAP1 layer (not shown). The AP2 layer which is also referred to as theouter pinned layer is formed on the AFM layer 12 and may be made of CoFewith a thickness of about 10 to 50 Angstroms. The magnetic moment of theAP2 layer is pinned in a direction anti-parallel to the magnetic momentof the AP1 layer. For example, the AP2 layer may have a magnetic momentoriented along the “+x” direction while the AP1 layer has a magneticmoment in the “−x” direction. A slight difference in thickness betweenthe AP2 and AP1 layers produces a small net magnetic moment for thepinned layer 13 along the easy axis direction of the TMR sensor to bepatterned in a later step. The AP1 layer may be comprised of CoFe,CoFeB, or a combination thereof.

Above the pinned layer 13 is a non-magnetic spacer. In one embodiment,the non-magnetic spacer 14 may be comprised of Cu or another metal togive a sensor 1 with a GMR configuration. In another aspect, a GMRsensor may have a current confining path (CCP) configuration in which adielectric material such as a metal oxide is sandwiched between twometal layers and has metal pathways therein to restrict the currentflowing between a first metal layer and second metal layer in adirection perpendicular to the planes of the metal layers.Alternatively, the non-magnetic spacer 14 may be comprised of adielectric material such as MgO, TiOx, AITiO, MgZnO, Al₂O₃, ZnO, ZrOx,or HfOx which results in a TMR configuration. In a TMR embodiment, a MgOlayer is preferably formed by depositing a first Mg layer on the pinnedlayer 13 and then oxidizing the Mg layer with a natural oxidation (NOX)or ROX process. Thereafter, a second Mg layer is deposited on theoxidized first Mg layer. Following a subsequent annealing step, thenon-magnetic spacer essentially becomes a uniform MgO tunnel barrierlayer as oxygen from the oxidized Mg layer diffuses into the second Mglayer.

The free layer 15 formed on the non-magnetic spacer 14 may be made ofCoFe, CoFeB, NiFe, or a combination thereof. Optionally, otherferromagnetic materials may be selected as a single component free layeror in a composite with one or more of CoFe, CoFeB, and NiFe. The widthof the free layer 15 along the ABS to be formed in a subsequent lappingstep is a critical dimension that controls the performance of thesensor. In general, a smaller FLW and track width will enable a higherrecording density in the sensor device. Track width is understood tomean the distance between the leads (not shown) along the top surface ofthe capping layer 16. In an embodiment wherein the sidewall 18 isessentially vertical with respect to substrate 10, track width isconsidered to be equal to FLW. On the other hand, the sidewall may besloped such that the width of the top surface of capping layer 16 isless than the width of the seed layer 11 at the ABS in which case trackwidth is less than FLW.

The capping layer 16 is employed as the uppermost layer in the MTJ stackand may be comprised of Ta, Ru/Ta, or Ru/Ta/Ru, for example. All layersin the MTJ stack may be deposited in a DC sputtering chamber of asputtering system such as an Anelva C-7100 sputter deposition systemwhich includes ultra high vacuum DC magnetron sputter chambers withmultiple targets and at least one oxidation chamber. Typically, thesputter deposition process involves an argon sputter gas and a basepressure between 5×10⁻⁸ and 5×10⁻⁹ torr. A lower pressure enables moreuniform films to be deposited. The present invention also anticipatesthat the capping layer 16 may include one or more hard mask materialsthat have specific etch rates during IBE, RIE, and CMP processes tooptimize the MTJ stack profile and improve resistance to erosion.

Once all of the layers 11-16 in the MTJ stack are laid down, the MTJstack may be annealed by heating to a temperature between about 250° C.to 350° C. for a period of 2 to 10 hours while a magnetic field isapplied along a certain direction to set the magnetic direction for thepinned layer and free layer. For example, if the easy axis direction isintended to be along the x-axis direction, a magnetic field may beapplied along the x-axis during the annealing step.

As a first step in the MTJ patterning process, a photoresist layer 17 iscoated on the top surface of the capping layer 16 and patterned to forma plurality of shapes such as islands in the form of circles or ovalsfrom a top view (not shown). The width of a photoresist shape from a topview following the patterning step is referred to as the photo CD and isusually measured by a CD-scanning electron microscope (SEM). The patternis then transferred through the MTJ stack of layers with an etch processthat is preferably a reactive ion etch (RIE). As a result, sidewall 18is formed at the edge of the MTJ stack of layers 11-16. In a preferredembodiment, the sidewall is essentially vertical (perpendicular to thesubstrate 10) and the photo CD in the photoresist layer is replicated inthe MTJ stack of layers. However, the present invention also anticipatesthat the sidewall 18 may have a slope wherein the width of the cappinglayer 16 is less than the width of the seed layer 11 along the x-axisdirection.

A key feature of the present invention is a multiple step IBE sequencethat is employed to trim the initial FLW shown as w1 to a substantiallysmaller value depicted as w4 (FIG. 5). It should be understood thattrack width (TW) may be less than FLW because TW is measured at the topsurface of the MTJ stack that has a CD≦FLW. The IBE sequence isperformed in such a manner that the magnetic properties including Hc andRA in the partially formed magnetoresistive sensor in FIG. 1 aresubstantially maintained in the trimmed sensor stack (FIG. 5) while theMR ratio is significantly enhanced compared with a conventional singleIBE trim method or a two step trim sequence involving different IBEincident angles.

According to the multiple IBE sequence of the present invention, allthree IBE steps are preferably performed in the same chamber of an IBEtool to optimize throughput. A first IBE step (FIG. 1) is performed withan ion beam 20 having a low energy of <300 eV that is directed atsidewall 18 at an incident angle α of greater than 0 degrees but lessthan 20 degrees with respect to a plane that is vertical to thesubstrate 10. In other words, ion beam 20 has a primary component thatis perpendicular with respect to the substrate and to MTJ element topsurface 16 s. The steep angle IBE etch is employed to remove 60% to 90%of the total FLW (critical dimension) to be trimmed during the entireIBE sequence. Therefore, a majority of the trimmed width represented by(w1−w4) is removed during the first IBE step. In one aspect wheresidewall 18 is vertical, the trimming occurs at an essentially equalrate independent of the location on sidewall 18. However, when sidewall18 is sloped at an angle that is not vertical, trimming may selectivelyoccur along a wider section of the MTJ element to produce a morevertical sidewall. Preferably, the ion beam 20 is generated from aninert gas such as Ar, Ne, or Xe with conditions comprising a flow rateof 10 to 50 standard cubic centimeters per minute (sccm) flow rate, anion current between 100 and 600 mA, and a RF power from about 100 to 600Watts. As a result, a considerable amount of residue tends to beredeposited on the sidewall 18.

Referring to FIG. 2, the FLW is w2 following the first IBE step wherew2<w1. A second IBE step is performed with an incident beam 21 that isgenerated with an inert gas and a low energy of less than about 300 eV.It is important that the incident beam 21 impinge on sidewall 18 at anangle β of between 60 and 90 degrees with respect to a plane that isperpendicular to substrate 10 and to MTJ element top surface 16 s. Ionbeam 21 is said to have a primary component that is parallel withrespect to the substrate. A second critical factor is the ion beam 21 isdirected at the sidewall 18 with a sweeping motion to remove the residuefrom the first IBE step and to further trim the FLW to a width w3. Thehigh incident angle is necessary for efficient side trimming of sensor1.

Referring to FIG. 3, a top-down view of the partially formedmagnetoresistive sensor is shown to illustrate the sweeping motion ofthe ion beam 21 during the second IBE step. In the exemplary embodiment,the photoresist mask layer 17 (and underlying sensor) has a circularshape. The second IBE step comprises rotating the ion beam 21 in acounterclockwise direction 40 a for up to about 40 degrees and thenreversing the movement in a clockwise direction 40 b over the same arcof up to about 40 degrees. Optionally, the first movement from astarting position may be a clockwise rotation 40 b followed by acounterclockwise motion 40 a back to the starting position. The sweepingmotion that includes movement 40 a followed by movement 40 b, or viceversa, is repeated a plurality of times (cycles) at a sweep rate of 5 to10 cycles per minute. We have discovered that between 3 and 10 sweepcycles are necessary for efficient residue removal from sidewall 18.

Referring to FIG. 4, the partially formed magnetoresistive sensor havinga FLW=w3 is then treated with a third IBE step that comprises a lowenergy less than 300 eV and a low incident angle δ greater than 0degrees but less than 20 degrees with respect to a plane formedperpendicular to substrate 10. Thus, ion beams 22 are directed towardsidewall 18 at a steep angle and remove about 10% to 40% of the width(w1−w4) to be trimmed during the entire multiple step IBE sequence. Ionbeam 22 has a primary component that is perpendicular with respect tosubstrate 10 and MTJ top surface 16 s. The third IBE step serves animportant function in that damaged portions of sidewall 18 resultingfrom the second IBE step are removed without causing further damage thatcould degrade magnetic properties of the magnetoresistive sensor 1. Inparticular, the third IBE step removes damaged portions of non-magneticspacer 13 that were exposed to ion beam 21 in the previous step therebypreserving a high MR ratio in both TMR and GMR embodiments. Thoseskilled in the art will appreciate that the x-axis component of ion beam22 in the third IBE step is sufficiently weak so as not to induce anysignificant damage to sidewall 18. Moreover, the y-axis (vertical)component of the third IBE step is primarily responsible for removingdamaged portions of sidewall 18 from the previous step.

Referring to FIG. 5, the magnetoresistive sensor has a final FLW of w4after the multiple step IBE sequence is completed. The advantage of theIBE trim sequence as described herein is that a FLW=w4 can bereproducibly formed with a value substantially less than 50 nm and incertain cases approaching 30 nm. In the prior art, FLW values ofsignificantly less than 50 nm cannot be reproducibly generated in amanufacturing environment. Thus, we have discovered a method thatenables sensor technology to move into critical dimensions approaching30 nm that will lead to a dramatic improvement in device performance.Furthermore, the slope of sidewall 18 may be manipulated to an anglethat ranges from 90 degrees with respect to substrate 10 to an angleless than 90 degrees where the width of capping layer 16 is less thanthe width of seed layer 11 along the ABS. In certain sensor designs, thesidewall slope is less than 90 degrees to avoid a tendency for MTJstacks with a high aspect ratio (height/width) to collapse during ionmilling. The slope of sidewall 18 may be modified by changing theincident angle of one or more of the three IBE steps during the IBE trimsequence. In particular, the second IBE step may be optimized togenerate an angle that is more vertical for sidewall 18 with respect tosubstrate 10.

Referring to FIG. 6, fabrication of a read head that includesmagnetoresistive sensor 1 may follow a conventional pathway. Accordingto one embodiment, a seed layer 19 having a top surface 19 s may bedeposited on substrate 10 and adjacent to sidewall 18. Thereafter, ahard bias layer 24 with sufficient thickness for providing longitudinalbiasing to free layer 15 is formed on seed layer 19. Electrical leads 25are formed on hard bias layer 20. Once the photoresist mask 17 isremoved by a lift-off process, for example, a second gap layer 26 andsecond shield (S2) 27 may be sequentially formed on the top surface 16 sof capping layer 16. In this embodiment, sidewall 18 is shown with aslope unequal to 90 degrees. In an alternative embodiment (not shown),sidewall 18 may have a vertical slope with respect to substrate 10 inorder to enable a maximum density in the MTJ array formed on thesubstrate. It should be understood that the present inventionencompasses other hard bias configurations and is not limited to theembodiment depicted in FIG. 6.

Example 1

In order to demonstrate the benefits of the multiple step IBE sequenceof the present invention, a TMR sensor was fabricated according to amethod previously practiced by the inventors, and according to anembodiment as described herein. For each of the wafers 1, 2, and 3, abottom spin valve configuration was formed on a AlTiC substrate and isrepresented by Ru/Ta/IrMn/CoFe/Ru/CoFeB/MgO/CoFeB/Ru/Ta where Ru/Ta isthe seed layer, IrMn is the AFM layer, CoFe/Ru/CoFeB is the pinnedlayer, MgO is a tunnel barrier layer, CoFeB is the free layer, and Ru/Tais a composite capping layer. Data was collected for circular shapeddevices as described below.

Wafer 3 is a reference sample that is a sensor made by a prior artmethod in which the FLW formed after pattern transfer through the sensorstack of layers is trimmed with a single IBE step comprising an incidentangle of 8 degrees with respect to a plane formed perpendicular to thesubstrate. As shown in Table 1, the sensor on wafer 3 is capable ofachieving a RA=1.2 ohm-μm² and a dR/R=62%. Referring to FIG. 7, CDmeasurements obtained from wafer 3 are represented by the diamondshapes. The data indicates, for example, when FLW=52 nm (point 50) afterthe initial pattern formation (Photo CD), the minimum trimmed FLW valueachieved is about 43 nm for a reduction of 9 nm when a single IBE trimstep is employed. Similarly, a 61 nm CD after pattern transfer isreduced to about 52 nm (point 52) following a single IBE step. Photo CDmeasurements were obtained using a CD-SEM and FLW measurements are takenfrom transmission electron microscopy (TEM) cross-sections.

TABLE 1 Effect of IBE conditions on magnetic properties ofNiCr/IrMn/CoFe/Ru/CoFeB/MgO/CoFeB/Ru/Ta/Ru TMR sensors Normalized WaferIBE Condition RA dR/R dR/R 1 8 deg. angle, 100% trim + 70 deg. 1.2 48%0.77 sweep 2 8 deg. angle, 80% trim + 70 degree 1.2 61% 0.98 sweep + 8degree angle, 20% trim 3 8 deg. angle, 100% trim 1.2 62% 1.0

Wafer 1 is a modification of Wafer 3 in that a first IBE step involvingan incident ion beam angle of 8 degrees with respect to vertical isemployed to trim the FLW to the desired width. In addition, a second IBEstep with a 70 degree sweeping motion is used to remove residue from thefirst IBE step. Note that Wafer 3 does not represent an acceptablemanufacturing process because residue remains after a single IBE trimstep. Since no third IBE step is included for Wafer 1, some damageoccurs to the exposed portions of the sensor sidewalls and especially tothe MgO tunnel barrier which causes an undesirable decrease in dR/R to48% even though RA is maintained at 1.2 ohm-μm².

Wafer 2 is produced according to an IBE sequence of the presentinvention wherein step 1 comprises an incident beam angle of 8 degreeswith respect to a vertical plane to shrink the FLW to by about 80% ofthe desired amount. In the following step 2, an ion beam at a 70 degreeincident angle is applied in a sweeping motion to remove residue fromstep 1. Finally, step 3 comprises another 8 degree incident angle IBE ata low energy of <300 eV to shrink FLW by the final 20% of the desiredamount. In so doing, the FLW can be decreased by about 20 nm from aPhoto CD of 53 nm to final CD of 35 nm (Point 51) or from a Photo CD of62 nm to a final CD of 40 nm (Point 53). In other words, a criticaldimension reduction of about 20 nm from an initial Photo CD in the rangeof 50 nm to 70 nm can be achieved by following a three step IBE processof the present invention. RA is maintained at 1.2 ohm-μm² while dR/R=61%is essentially equivalent to the value of 62% achieved after a singleIBE trim step. Thus, the three step IBE sequence of the presentinvention offers an advantage in realizing a smaller sensor CD thanpreviously realized without degrading any other magnetic propertiesincluding RA and dR/R. It should be understood that a similar CDreduction of around 20 nm can also be achieved when starting with aPhoto CD greater than 70 nm. However, the present invention is mostadvantageous in an embodiment wherein the Photo CD is less than 70 nm sothat FLW dimensions of less than 50 nm may be fabricated with higheryields and better reliability for advanced devices.

The three step IBE sequence as disclosed herein may be readilyimplemented in existing manufacturing lines since no new tools ormaterials are required. Furthermore, the process can be applied tosensor devices of older technology products where there is evidence ofdamage from a two step IBE process thereby improving magnetic propertiesof CIP-GMR, CPP-GMR, and TMR sensors where CIP refers tocurrent-in-plane and CPP means current perpendicular to plane.

While this invention has been particularly shown and described withreference to, the preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of this invention.

1. A method of reducing a critical dimension in a magnetoresistivesensor, comprising: (a) providing a magnetic tunnel junction (MTJ) stackof layers on a substrate including a pinned layer, a free layer, anon-magnetic spacer between the pinned layer and free layer, and anuppermost capping layer; (b) patterning the MTJ stack of layers to forma MTJ element having a top surface and a sidewall that connects the topsurface with the substrate, said free layer has a critical dimensionwhich is a first width along a plane that is parallel to the MTJ elementtop surface; (c) performing a first low energy ion beam etch (IBE) stepwith an ion beam incident angle less than about 20° with respect to aplane perpendicular to the substrate to trim the sidewall such that thefree layer has a second width less than the first width; (d) performinga second low energy IBE step with a sweeping motion and with an ion beamincident angle greater than about 60° with respect to a planeperpendicular to the substrate to remove residue formed during the firstIBE step and further trim the sidewall such that the free layer has athird width less than the second width; and (e) performing a third lowenergy IBE step with an ion beam incident angle less than about 20° withrespect to a plane perpendicular to the substrate to remove damagedportions of the sidewall resulting from the second IBE step and tofurther trim the sidewall such that the free layer has a final widthless than the third width.
 2. The method of claim 1 wherein the lowenergy IBE steps comprise an inert gas and an energy less than about 300eV.
 3. The method of claim 2 wherein the IBE steps comprise an ioncurrent between about 100 and 600 mA and a RF power from about 100 to600 Watts.
 4. The method of claim 1 wherein the sweeping motioncomprises a first movement of rotating the substrate within an arc ofabout 40 degrees in a clockwise or counterclockwise direction from astarting position followed by a second movement of rotating thesubstrate in the opposite direction back to the starting position, saidfirst and second movements are repeated a plurality of times.
 5. Themethod of claim 1 wherein the first IBE step is responsible for about60% to 90% of a critical dimension reduction represented by (firstwidth−final width).
 6. The method of claim 1 wherein the third IBE stepis responsible for about 10% to 40% of a critical dimension reductionrepresented by (first width−final width).
 7. The method of claim 1wherein the first width is from about 50 to 70 nm and a criticaldimension reduction represented by (first width−final width) is about 20nm.
 8. The method of claim 1 wherein the MTJ element is a CIP-GMR,CPP-GMR, or a TMR sensor.
 9. The method of claim 1 wherein the sidewallhas an angle with respect to the substrate that may be changed byvarying the incident angle during one or more of the three IBE etchsteps.
 10. The method of claim 9 wherein the MTJ element has a trackwidth essentially equal to the final width when the sidewall angle isabout 90 degrees.
 11. A method of reducing a critical dimension in amagnetoresistive sensor, comprising: (a) providing a magnetic tunneljunction (MTJ) stack of layers on a substrate including a seed layer,AFM layer, pinned layer, free layer, non-magnetic spacer between thepinned layer and free layer, and an uppermost capping layer; (b)patterning the MTJ stack of layers to form a MTJ element having a topsurface and a sidewall that connects the top surface with the substrate,said free layer has a critical dimension which is a first width along aplane that is parallel to the MTJ element top surface; (c) performing afirst low energy ion beam etch (IBE) step with an ion beam incidentangle that has a primary component which is perpendicular with respectto the substrate to trim the sidewall such that the free layer has asecond width less than the first width; (d) performing a second lowenergy IBE step with a sweeping motion and with an ion beam incidentangle that has a primary component which is parallel with respect to thesubstrate to remove residue formed during the first IBE step and furthertrim the sidewall such that the free layer has a third width less thanthe second width; and (e) performing a third low energy IBE step with anion beam incident angle that has a primary component which isperpendicular with respect to the substrate to remove damaged portionsof the sidewall resulting from the second IBE step and to further trimthe sidewall such that the free layer has a final width less than thethird width.
 12. The method of claim 11 wherein the low energy IBE stepscomprise an inert gas and an energy less than about 300 eV.
 13. Themethod of claim 12 wherein the IBE steps comprise an ion current betweenabout 100 and 600 mA and a RF power from about 100 to 600 Watts.
 14. Themethod of claim 11 wherein the sweeping motion comprises a firstmovement of rotating the substrate within an arc of about 40 degrees ina clockwise or counterclockwise direction from a starting positionfollowed by a second movement of rotating the substrate in the oppositedirection back to the starting position, said first and second movementsare repeated a plurality of times.
 15. The method of claim 11 whereinthe first IBE step comprises an incident angle of greater than 0 degreesand less than 20 degrees with respect to a plane perpendicular to thesubstrate, and is responsible for about 60% to 90% of a criticaldimension reduction represented by (first width−final width).
 16. Themethod of claim 11 wherein the second IBE step comprises an incidentangle of greater than about 60 degrees and less than 90 degrees withrespect to a plane formed perpendicular to the substrate.
 17. The methodof claim 11 wherein the third IBE step comprises an incident anglegreater than 0 degrees and less than 20 degrees with respect to a planeperpendicular to the substrate, and is responsible for about 10% to 40%of a critical dimension reduction represented by (first width−finalwidth).
 18. The method of claim 11 wherein the first width is from about50 to 70 nm and a critical dimension reduction represented by (firstwidth−final width) is about 20 nm.
 19. The method of claim 11 whereinthe MTJ element is a CIP-GMR, CPP-GMR, or a TMR sensor.
 20. The methodof claim 11 wherein the sidewall has an angle with respect to thesubstrate that may be changed by varying the incident angle during oneor more of the three IBE etch steps.